It's hard to estimate a reasonable price for this if you don't have any revenues. Whereas you could usually discount future cash flows, in this case you would need to estimate the goodwill - which probably means what you're willing to pay for maintaining this site as a hobby.

BTW. does this page still get a lot of hits? I've seen on my past projects (albeit on a much smaller scale) that those services usually spike for a few days and then quickly die off - what are the current usage statistics?